The present invention relates to a seesaw switch of the type in which a movable contact piece performs a seesaw motion, by the actuation of a push button or toggle lever, with the fulcrum at a common contact to turn into or out of contact with at least one fixed contact provided opposite the common contact.
A conventional push-button seesaw switch usually has such a structure as shown in FIG. 1 in which a movable contact piece 1 is actuated, by the depression of a push button 11, to perform a seesaw motion with the fulcrum at a common contact 2. The switch closes as the movable contact piece 1 merely abuts against a fixed contact, and opens as they break.
The seesaw switch is commonly used to open or close a circuit which is supplied with relatively high voltage and current, for example, 4 to 5 volts or more and several tens of milliamperes. In such a circuit, even if oxide films are formed on the contacts, they are destroyed by a spark discharge which develops owing to current and voltage as the contacts make or break, and the intended contact can be maintained. Where the frequency of operations of the switch is relatively high, the possibility of an oxide film being formed is slight.
When a push-button switch of the type shown in FIG. 1 is used in a circuit which provides a start signal to a device formed by semiconductor integrated circuits, the voltage and current that are handled in such a circuit are so small that a spark discharge hardly occurs as the contacts make and break. Therefore, the formation of oxide films on the contacts would immediately lead to bad contact therebetween since there is no provision in the switch for destroying the films. Moreover, when the push-button switch is used as a start switch or the like, since the frequency of operation is relatively low, oxide films are liable to be formed on the contacts.
To avoid this, in the case of employing the pushbutton switch for a very weak current and voltage circuit, it is customary in the prior art to plate its contacts, that is, the movable contact piece 1 and the fixed contacts 3, with gold so that no oxide films are deposited on the contacts. This, however, increases the manufacturing costs of the switch, and hence is disadvantageous from the economical point of view.
Even if the contacts are plated with gold, dust or like foreign matter sticking to the contacts may sometimes cause bad contact since the switch has no provision for removing the dust or the like.
Occasionally the situation arises where a plurality of seesaw switches of the toggle lever type are disposed side by side to constitute a digital setting arrangement. When the seesaw switch is used as a digital setting switch, the frequency of operation is lower than in the case where it is used as the aforesaid start switch; therefore, it is more likely that oxide films are formed on the contacts. A conventional solution to this problem is also to plate the switch contacts with gold, but this is economically disadvantageous, as mentioned above.
To overcome the above disadvantage, Japanese Utility Model Public Disclosure No. 195735/82 gazette proposes a fully-enclosed, sliding contact type switch in which a clip-like movable contact piece 4 is provided in a manner to be slidable on the fixed contacts 3 and is actuated by a toggle lever 5, as shown in FIG. 2.
With such a sliding contact type switch, since the movable contact piece moves into or out of contact with the fixed contacts while sliding thereon, even if oxide films are formed on the contacts, they are torn off by the relative sliding movement of the contacts, providing what is called a self-cleaning action. Accordingly, the sliding contact type switch can be used with a very weak current and voltage circuit without the necessity of plating the contacts with gold.
Incidentally, the sliding contact structure is generally used in many slide switches, and the movable contact piece 4 is the most stable in operation when adapted to move horizontally along an insulating plate 6 on which the fixed contacts 3 are planted.
In the switch disclosed in the aforementioned Japanese utility model gazette, however, since the movable contact piece 4 is driven directly by the pivotal movement of the toggle lever 5, it is difficult to match the movement of the movable contact piece 4 and the movement of the toggle lever 5. The reason for this is that since the tip of the toggle lever moves in a circular arc, the gap between the insulating plate 6 supporting the fixed contacts 3 and the toggle lever 5 varies with the pivotal movement of the latter. This difficulty could be overcome by concaving the insulating plate 6 in conformity to the circular arc along which the tip of the toggle lever moves, but this presents a problem of increased manufacturing costs of the insulating plate 6.
It is therefore a primary object of the present invention to provide a seesaw switch in which a movable contact piece moves into or out of contact with a fixed contact while sliding thereon to provide a self-cleaning action, ensuring to maintain stable contact therebetween for a long period of time.
Another object of the present invention is to provide a highly durable seesaw switch in which a movable contact piece performs a seesaw motion regardless of whether the actuator is of the push-button or toggle lever type, thereby ensuring proper operation of the contact change-over mechanism.